1. Field of the Invention
The present invention relates to a semiconductor pressure sensor and a fabrication method thereof, particularly a semiconductor pressure sensor including a MOS circuit, and a method of fabricating such a semiconductor pressure sensor.
2. Description of the Background Art
In recent years, semiconductor pressure sensors are used in various fields such as in vehicles. One known type of a semiconductor pressure sensor is integrated with a complementary metal oxide semiconductor (MOS) circuit. A semiconductor pressure sensor disclosed in PTD 1 (Japanese National Patent Publication No. 2004-526299 (Japanese Patent No. 4267322)) will be described as such type of a semiconductor pressure sensor.
The semiconductor pressure sensor has a region where a MOS circuit is formed (MOS region) and a region where a pressure sensor is formed (pressure sensor region), defined at a semiconductor substrate. At the MOS region, an n-channel type MOS transistor and a p-channel type MOS transistor constituting a MOS circuit are formed.
At the pressure sensor region, a capacitive type pressure sensor is formed. The capacitive type pressure sensor includes a fixed electrode and a movable electrode, and has a vacuum chamber provided between the fixed electrode and the movable electrode. The vacuum chamber is sealed by a sealing film. The pressure is measured by detecting the change in the distance between the movable electrode and fixed electrode as a function of the capacitance value.
A conventional semiconductor pressure sensor has a problem set forth below. For the semiconductor pressure sensor, the step of forming a pressure sensor and the step of forming a MOS circuit are provided separately. In other words, the step of forming a sealing film to provide a vacuum chamber is additionally required as a dedicated step to producing a pressure sensor.
When a sacrifice film is to be removed by etching, a protection film for protecting the MOS region must be provided before that step, and the protection film must be removed after removal of the sacrifice film. Furthermore, in view of the vacuum chamber arranged below the movable electrode being formed prior to forming a metal interconnection at which the MOS region process is completed, sticking countermeasures are required to prevent the movable electrode from sticking caused by a wetting process or the like. This induces the problem that the fabrication process is lengthened and rendered complicated for a conventional semiconductor pressure sensor.